A typical fiber optic backplane includes a network of optical fibers. Typically, each optical fiber conveys light signals (pulses of light) from one location of the backplane to another.
One conventional fiber optic backplane includes a rectangle-shaped central portion, and multiple ribbon portions which extend in parallel from one side of the central portion. Optical fibers within each ribbon portion continue through the central portion and out through one or more other ribbon portions. Accordingly, when the fiber optic backplane is in operation, light signals sent through fibers of one ribbon portion continue within those fibers through the central portion and out one or more of the other ribbon portions.
The central portion of the fiber optic backplane typically includes (i) an outer covering which resembles a plastic laminate, (ii) portions of optical fibers, and (iii) an adhesive fluid that tends to prevent movement of the optical fibers within the outer covering. The ribbon portions of the fiber optic backplane typically include portions of the same outer covering used in the central portion, and portions of optical fibers running therebetween. The outer covering and fluid holds the optical fibers in place and tends to prevent their movement among each other.
To form the fiber optic backplane, a manufacturer typically lays down an adhesive-backed sheet of the outer covering to form a bottom layer of the backplane. Next, the manufacturer runs portions of optical fibers over that sheet along desired optical fiber paths. Then, the manufacturer adds the fluid and lays down another sheet of the outer covering to form a top layer of the backplane. Finally, the manufacturer seals the top and bottom sheets together (e.g., by applying heat) and cuts the sheets to form the central portion and the connected ribbon portions. The fiber optic backplane, which is soft and flexible, can then be clipped to a rigid board and connected between multiple fiber optic components (e.g., circuit boards, fiber optic cables, etc.) to convey light signals among the components.
When two optical fibers cross over each other, one of the optical fibers typically bends around the other. The light energy loss through the bent optical fiber increases as the bend radius of at optical fiber increases (i.e., the sharper the bend, the more light energy loss). Since the effectiveness of fiber optic signal detection circuitry (e.g., light sensing circuitry) is best when light energy loss is minimal, manufacturers try to limit the number of optical fibers crossing over each other at any single point in the backplane. To this end, fiber optic backplane manufacturers typically arrange the portions of optical fibers within each ribbon portion in rows to prevent the optical fibers from crossing over each other within that ribbon portion, and position all of the optical fiber cross-over occurrences in the central portion. Additionally, manufacturers try to limit the number (e.g., less than eight) of optical fibers crossing at any one point in the central portion since a high number of optical fibers crossing over each other at a particular point tends to result in more severely bent fibers (i.e., the optical fiber at the top tends to have the sharpest bend and typically experiences the most light energy loss). Furthermore, manufacturers attach the ribbon portions to the central portion far enough apart from each other (e.g., several centimeters) so that light energy loss due to optical fibers bending within the central portion from one ribbon portion to another is not excessive.
Insulated optical fibers (e.g., individual rubber protected optical fibers) typically extend individually from the far ends of the ribbon portions of the fiber optic backplane. Each optical fiber typically terminates at a respective fiber optic connector that provides the optical fiber end as an optical interface for forming a fiber optical connection with the end of another optical fiber. Typically, the fiber optic backplane connectors employ rigid elbow-shaped (e.g., 90 degree arc) strain reliefs. Accordingly, a technician can easily mate and un-mate the fiber optic connectors with other fiber optic connectors (e.g., corresponding fiber optic connectors mounted to a rigid board) to form individual fiber optic connections with other components.
Unfortunately, there are deficiencies to the above-described conventional fiber optic backplane. In particular, the number of fibers through the backplane (e.g., the number of fibers in a particular ribbon portion, the number of fibers in a terminating connector, etc.) is relatively low since the density of the backplane is limited by the number of fibers crossing over each other in the central portion. If there are too many fibers crossing over each other in the fluid-filled central portion at a particular point, some of the optical fibers passing through the central portion will tend to be pulled by the laminate and any external forces. In particular, the fibers on top (i.e., the top fibers on cross-overs of many fibers) will tend to be pulled down the most. In some situations the fibers will bend sharply resulting in excessive light energy loss.
Furthermore, density is low since the ribbons are disposed side-by-side from the central portion thus limiting the number of fibers in the ribbons to the available edge length of the central portion. This deficiency makes scaling difficult.
Additionally, in some situations, density is low due to restrictions on how close the ribbons can be placed next to each other. For example, if the ribbon portions of the backplane are too close together, the fibers may be forced to bend sharply within the central portion and result in excessive light energy loss. Also, the manufacturer may need to provide certain clearances between ribbon portions in order to properly cut the laminate (e.g., clearance that allow a laser to cut out the ribbon portions).
Furthermore, the termination of the ribbon portions with individual fiber optic connectors holding single fiber ends limits the fiber optic backplane to low density applications. That is, the fiber optic backplane is poorly suited for more complex routing situations that require many fibers running in many different directions. The alternative is for a technician to connect and/or combine multiple fiber optic backplanes, or to use a tangled network of fiber optic cables that carry bundles of optical fibers (in place of the fiber optic backplane) for these more complicated connection tasks.
In contrast to the above-described conventional fiber optic backplane which has parallel ribbon portions extending from different locations of a central portion (e.g., locations that are several centimeters apart along a side of the central portion), the invention is directed to fiber optic connection techniques which use a fiber optic backplane having a casing portion and multiple fiber optic ribbons that extend from the same location of the casing portion. The invention is well-suited for higher density situations and can be implemented without significant light energy loss.
One arrangement of the invention is directed to a fiber optic backplane that includes multiple optical fibers, a casing and a set of ribbon coatings. The casing holds casing portions of the optical fibers. The set of ribbon coatings holds ribbon portions of the optical fibers in rows to form multiple optical fiber ribbons. Each ribbon coating of the set of ribbon coatings attaches to the casing at a same location of the casing such that the optical fiber ribbons extend from that same location of the casing. The multiple optical fiber ribbons which extend from the same casing location enable higher optical fiber densities than conventional fiber optic backplanes which only have parallel ribbon portions extending from different locations of a central backplane portion (e.g., locations which are centimeters apart).
In one arrangement, another set of ribbon coatings holds other ribbon portions of the optical fibers in rows to form other optical fiber ribbons. Each ribbon coating of the other set of ribbon coatings attaches to the casing at another location of the casing such that the other optical fiber ribbons extend from the other location of the casing. Accordingly, the fiber optic backplane can have multiple sets of optical fiber ribbons, e.g., a first set extending from one location, a second set extending from another location (perhaps in parallel with the first set), and so on.
In one arrangement, a cross-section of each optical fiber ribbon is substantially planar in an X-direction, and an end of each optical fiber ribbon of the multiple optical fiber ribbons is aligned in a column that extends in a Y-direction that is substantially perpendicular to the X-direction. This arrangement provides for stacking of optical fiber ribbons which is a convenient and well-organized technique for arranging the optical fibers.
In one arrangement, the casing includes a flexible polymer skin (e.g., a thick plastic coating) that is capable of elastically deforming under stress. In this arrangement, a viscous glue is preferably retained around portions of the optical fibers by the flexible polymer skin of the casing. The viscous glue assists in suspension of the optical fibers thus minimizing any bending of the optical fibers at the optical fiber cross-over points within the casing. Accordingly, there is minimal light energy loss within the casing due to optical fibers crossing over each other even when the number of optical fibers crossing over each other at a particular point is relatively high (e.g., eight or greater).
In one arrangement, the casing includes a rigid member that covers the casing portions of the optical fibers. Preferably, the rigid member of the casing defines a mounting surface onto which fiber optic components are capable of rigidly mounting. In this arrangement, fiber optic components (e.g., fiber optic connectors, fiber optic circuit boards, assorted housings and support members, etc.) have a rigid surface on which to mount.
In one arrangement, a set of fiber optic connecting members (e.g., ferrules, connectors, etc.) is coupled to the set of ribbon coatings. Each fiber optic connecting member positions ends of the ribbon portions of the optical fibers in a respective row. This arrangement enables the ends of the optical fibers to reside in higher density connectors relative to the ends of the optical fibers of a conventional fiber optic backplane which individually reside in separate connectors.
Another arrangement of the invention is directed to a fiber optic network assembly. The assembly includes fiber optic circuit boards and a fiber optic backplane that connects with the fiber optic circuit boards. Each fiber optic circuit board has a set of fiber optic circuit board connecting members. The fiber optic backplane includes multiple optical fibers, a set of ribbon coatings that holds ribbon portions of the optical fibers in rows to form multiple optical fiber ribbons, and a casing that holds casing portions of the optical fibers. Each ribbon coating of the set of ribbon coatings attaches to the casing at a same location of the casing such that the optical fiber ribbons extend from the same location of the casing. The backplane further includes a set of fiber optic backplane connecting members coupled to the set of ribbon coatings. Each fiber optic backplane connecting member positions ends of the ribbon portions of the optical fibers in a respective row and is capable of forming a set of optical connections with a corresponding fiber optic circuit board connecting member. As such, the assembly is capable of forming a computer system (with operating circuitry on the circuit boards), or at least a portion of a computer system.
Another arrangement of the invention is directed to a method for forming a fiber optic backplane. The method includes the steps of providing a support structure that defines channels, and positioning a set of ribbon coatings such that each ribbon coating of the set of ribbon coatings extends from a same channel defined by the support structure. Additionally, the method includes the step of distributing optical fibers such that ribbon portions of the optical fibers extend over the set of ribbon coatings, and support structure portions of the optical fibers extend through the channels defined by the support structure. The method further includes the step of securing the optical fibers such that (i) the set of ribbon coatings holds the ribbon portions of the optical fibers in rows to form multiple optical fiber ribbons that extend from the same channel defined by the support structure, and (ii) the support structure retains the support structure portions of the optical fibers. This method provides a simple and convenient way to manufacture the above-described fiber optic backplane in a controlled and consistent manner.
The features of the invention, as described above, may be employed in fiber optic systems, devices and methods and other computer-related components such as those manufactured by Teradyne, Inc. of Boston, Mass.